Transmission system



2 Sheets-Sheet l H. A. AFFEL TRANSM S S I ON SYSTEM Filed May 3l, 1929 Aug. 19, 1930.

Aug. 19, 1930. H. A. AFFEL TRANSMISSION I SYSTM Filed may 51, 1929 2 sheets-sheet` mm. LSSNSNE Patented Aug. 19,. 1930 UNITED sTATEs PATENT OFFICE l HERMAN A. AFFEL, F BIDGEWOOD, NEW JERSEY, ASSIGNOB TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK TRANSMISSION SYSTEM Application led Hay 31,

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The requirements for transmission over a telephone circuit are ordlnarily set to embrace a band width which 'includes all the frequencies required for speech transmission at an instant. It has been found that a band widt of about 3,000 cycles gives a very. fair artcu. lation reproduction for all speech sounds,

except certain of the sibilant and fricative consonants which re uire frequencies several thousands of cycles Olliigher for entirely adequate reproduction. In certain services, such as'transatlantic radio and very long undersea cables, an adequate band with -of even] 3,000 cycles maybe diicult and expensive to obtain. When 'a band width of only 2,000 or 1,500 cycles is available, transmission may be. carried on lonly with certain sacrifices in articulation.

It is one of the primary objects of-this in-m vention to provide arrangements for improving the transmission situation when only a' narrow band width of, for example, 1,000

cycles or 1,500 cycles can be economically obtained. In accordance with the *arrangey yments of the invention, provision is made so that, in the utilization of such narrow band, width, the voice range which is transmitted is varied upward or downward in frequency in accordance with the predominant frequencies present in the speech at the particular instant. For example, if a band width of 1,000 cycles were available for transmission4 over a long cable circuit, and if the speech at an instant re uired the transmission of a vowel sound em racing chiey frequencies Yfrom zero to 1,000 cycles, the available band width would be employed to transmit in its normal position the speechfffrequency from zero to '1,000 cycles. If, on the other hand,'the transmitted speech required a particular consonant reproduction, having a predominance of highfrequencies, such, for example` as the letters, the voice band would be shiftedy so that frequencies of say from 2,000 t 3,000 cycles would pass through the z'ero to 1,000

" er with the accompanyin 1929. serial No. 367,471.

cycle range provided by the cable.l The arrangements of the invention would operate in an automatic manner and in accordance with the speech requirements each instant. Further objects and features of the invention will appear more fully from the detailed descripmatic showing of means for affording two- Way operation with the apparatus of the invention. Similar reference characters have been utilized to denote like parts in all of the figures.

In F 1 is shown a circuit diagram ofA apparatus for sending messages in accord-y ance with the arrangements of this invention. Bridged across the circuit of the transmitter l is a roup of selective circuits. which includes the and filters F1, F2 and F3, therectitiers R1, ,R2 and Ra and the ma ets M1, M2 and MB. Each of the filters F1, 2 and Fa may be selective for a different band of frequencies in the message frequency band. For example, Fljmay pass Oto 1,000 c cles, F2 may pass 1,000 to 2,000 cycles, andli may pass 2,000 to 3,000 cycles. Networks for the urpose of weighting the different speech requencies in any desired manner may be incorporated in these filters or elsewhere `in the circuit. -The electromagnets control the armature 2 and the movement of the rotating plates of the variable condenser 3, whereby the capacity of the circuit 4 may be controlled. Thisl will control the variable frequency f of the modulator 5 in the .transmitter circuit. In the transmitter circuit will be a delay circuit 6. In the output circuit of the modulator 5 will be a band filter 7 and a modulator 8 with an oscillator of fixed frequency fd attached thereto. ed in the output of modulator 8 which will be connected to circuit 10 which may lead to ap- A high pass filter 9 will be connectparatus for transmitting signals, such as over a cable, radio or other circuit. Mountid onl the 'same shaftas the armature 2 of variable condenser 3 and hence controlled by magnets M1, lM2 and M2, is the contact member 12 of a potentiometer device comprising resistance 13 and battery 14. This arrangement will transmit variations in current magnitude and direction through 'low pass filter 11 to the circuit 10 for causing apparatus at a receivin station to operate in synchronism with t e sendin apparatus as will be more full described ereinafter.

T e message currents originating in transmitter 1, depending on pre ominance of particular frequencies at an instant, will actuate most powerfully one of the three mag.

nets M1, M2 or M2, which by its pull on the armature 2 of the variable condenser 3. will determine the exact capacit `introduced in circuit 4. This in turn wil determine the frequency, termed f, of the oscillator assol ciated with modulator 5 inthe l transmitter circuit. Modulator 5 acts to raise the fre.-` quency4 of the message after it has suffered a delay in circuit 6 inorder to allow for the required operating time of the electromagnets and variable condenser 3. The modulated voice currents are then assed through the filter 7, which will cute thellower side band and the other'unwa-nted pioducts of modulation, and the upper. side ndjisapplied to the modulator-8. This modulator will have a fixed frequency fd-and operate to step down the frequency ofthe transmits identical the voice band will pass throu h to the high pass filter 9 and thence to t e cable or radio circuit 10 without shifting its ition in the frequency range. However, if f is lower than fd, asv determined by an increase of the capacit of the variable condenser 3, the voice ban will be shifted downv cycles an ligger ward in position in such a manner that the hi her frequencies in the voice now appear as ower frequencies and are capable of transmission over the narrow band cable or radio channel.

For example, let it be assumed that at a ven instant the predominant frequencies in t e messa e band lie between zero and 1,000 that this band of frequencies is selected by filter F1 and actuates most strongly the electromagnet M1 to decrease theca-V pacity in circuit 4 so that f will equal fd and that the value of each will equal 10,000 cycles. The predominant portion of the message band, such as zero to 1,000 cycles, will then be modulated b f, or 10,000 cycles,'and the This will demodulated by fd, Vor 10,000 cycles, andthe result will be a band occupying in the frequency scale a range of 0 to 1,000 cycles. Let it be assumed that at another given instant the predominantfre- Side ban willy be 10,000 to 11,000 cyquencies in the message band lie between 1,000

2,000 cycles will be modulated by 9,000 cycles and the upper side band again will be 10,000 to 11,000 lcycles. When this is demodulated by fd, or 10,000 cycles, the result will be a band occupying the same range in the frequenc'y scale as heretofore, namely, from 0 to 1,000 cycles. Obviously, these values asv son.

sumed forf and fd are only for purposes of illustration, and other values may be utilized.

The invention provides means to insure a synchronous frequency shift in ythe reverse direction at thel receiving station so that no net frequency shift -is apparent at the receiver. For this purpose, a small portion of the lavailable frequency range is reserved for, a synchronizing or control channel and a circuit including a low pass lilter11 is connected to circuit 10. In the case where a cable cirf cuit is utilized for the transmission of the messa e, the control channel` will be transmitte by variations of current direction and magnitude from a source 'such as battery 14. The varying battery otentials will be applied to the low pass fi ter circuitand circuit 10 as determined by the potentiometer 12, 13, which, as has been pointedout, is connected to the same shaft as the armature 2 of s the variable condenser 3 and is controlled b ted side'band. If frequencies f and fd are the qperationof the electromagnets M1, 2 and 2 2. Any other desirable means forcontrol or synchronismmight be utilized if' the messages were to be sent over a radio or other circuit.

In Fig. 2 is shown receiving apparatus suitable for use with the arrangements of the invention. A circuit 15 is shown which may be connected to an incomin cable or radio circuit. Two branch circuits are connected to circuit15.A One of these circuits includes a low pass filter 22 and is for the control or synchronizing channel. The other circuit includes a high pass filter 16 and is for the message channel. The circuit for the control channel includes the. two magnets M4 and M5 which control the armature of a variable condenser 23. The armature of the variable condenser 23 in this case is polarized and its position and consequently the lcapacity of condenser 23 are determined by the direction and magnitude of thecontrol current transmitted over llO sending station, a band filter 18, and the modulator 19 having a variable frequency f. The oscillator circuit 24 of modulator 19 will have its frequency f varied by the condenser 23. By this double modulator arrangement, the voice band will be returnedv to its normal position in the frequency scale for transmittal through the low pass filter 20 to receiver 21.

lFor example, let it be assumed that at a given instant the predominant frequencies in the voice band originating in transmitter 1 were from 1,000 to 2,000 cycles. It has been pointed vout that this band would be shifted so as to occupyduring transmission a range of from 0 to 1,000 cycles. Atthe receiving station, this band would be modulated in modulator 17 by the frequency fd, or '10,000 cycles,' and the upper side' band would .be 10,000 t'o 11,000 cycles. The'control channelwould cause condenser 23 to make the freuency-.f the sameas at the sending station at t is instant, and hence f would equal 9,000 cycles. The result of the modulation in modulator .19 would be a band occupyingi the range of 1,000 to 2,000 cycles. words, the voice band would be reshifted to its original position in the frequency scale for 'transmission to thereceiver 21.

In Fig. 3 is shown a modification of the sending apparatus of the invention; In this' modification, instead` of providing for a smooth variation of frequency as determined by the osition of a variable condenser as in Fig. 1 t ree distinct band shifts are provided by three independentcircuits. Connected to the transmitter 1 would be three independent circuits including the band filters F11, F12 and F13 each of which would select a diffe-r- .ent band of frequencies in the message band.

F11 might pass a band of 2,000 to 3,000 cycles, F12-a band `of 1,000 to 2,000, and F13 a band ofzero to 1,000 cycles. 'Recti fiers R11, R12 and R13 are connected to each of these` independent selective circuits and in turn are connected to the electromagnets M11, M12 and M13. These magnets will control the pivoted switch 37 whereby the circuit 40 maybecompletedthrougheither battery 38 or For example,

battery7 39 or without either of said batteries.

Accordingl the predominant frequencies 1n the origina message band at a given instant Will control the polarity and magnitude of the current in circuit 40. The magnitude and polarity of the current in circuit 40 will control the operation of magnets .1 and M1, which in turn will connect the rotary switch to either of the three selective circuits connected to the transmitter v1. In other Words, the predominancey of certain frequencies at a given instant in the message band will determine which of the three selective circuits is to be utilized. Each of these circuits will include a delay circuit, such as 25, 26 and 27. Connected in the circuit including lter F11 would be a modulator 28 having a frequency ln otherf', a filter 29 for selecting the upper side band of the product of modulation, a second modulator 30 rhaving a fixed frequency fel, and a Vlow pass filter 31. The values of f and fd lof modulation, a second modulator 34 having a fixed frequenc fd, anda low pass filter 35. The values of f and .fd would befchosen so j that the band of frequencies selected by filter F11 would be shifted in the frequency scale to the same predetermined lposition as the band selected by the previously mentioned circuit. The frequencies selected by' filter F13 would be transmitted in4v their normal osition in the frequency scale which,l would e the desired and available band. The frequency bands would be transmitted through the high vpass filter 42 to a cablefor radio circuit 43. The

-variations of potential and magnitude of the current in circuit`40 Awould be transmitted through the low pass filter 44- and transmitted over the circuit 43 to synchronously control receiving apparatus operated in a corres onding manner. y

, n Fig. 4, there is shown schematically arsation with the apparatus of this invention. The apparatus at one station only is shown.- The telephone transmitting and receiving apparatus 45 is shown connected to a circuit 47. This circuit'would normally be connected over the contacts' of relays 46 and 49 through' the receiving apparatus 48 to the cable or radio circuit; The receiving apparatus 48 might be similar to-that shown in Fig. 2. Bridged across circuit 47 is the circuit 51 including the 'rectifier R6 and the relays 46 rangements for permitting two- Way converand 49. These relays may be voice-operated and marginal. When speechl starts, theywill operate to connect circuit-47 throughtransmitting apparatus, such as that shown in Fi 1, to the cable or radio circuit. By ma ing relays 46 and 49 marginal, they will not operate falsely on incoming currents.

While the invention hasbeen disclosed as embodied in certain specific forms which are deemed desirable, it is pointed outv that these specific forms may be varied. .For example,

Athe message band might be split into more parts and the frequency range covered .be much wider than indicated.l Accordingly, the invention is capable .of embodiment in many other forms than those illustrated without departin from the spirit of the inventionas define by the appended claims.

What is claimed is: y

1.v The method of reducing the frequency band Width required for acommunication channel, which comprises selecting a'llportion lao ' which comprises selecting a portion of the message band in accordance with the frequencies predominant therein at a given instant, shiftmg the selected portion of said band to apredetermined position in the frequency scale, transmittin said selected portion of the band as shifte ,reshifting to its original position in the frequency scale said transmitted portion of the message band, and receiving said portion of the band.

4. The method 0f message transmission, which comprises successively selecting. portions of the message band in accordance with the frequencies predominant therein at successive lnstants, successively shiftingthe` selectedr portions ofsaid message band. to the same-position in the frequency scale, successivel transmitting said portions of the band as s ifted, successively reshifting to their original positions in the frequency scale said transmitted portions of the messa e band, and successively receivingsaid reshi ted portions of the band.

5. The method of message transmission, .which comprises successively selecting portions of the message band in accordance with the frequencies predominant therein at successive instants, successivelyshifting theselected portions of said message band to the Same position in the frequency scale, successivel transmitting said portions of the band as s ifted, 'successivelyv reshifting to their original positions in the frequency scale said transmitted portions of the message band,

synchronizing the shifting and reshfting of said portions of the message band, and suc; cessively receiving said reshifted .portions of the band.

6. The method of telephone transmission, which comprises selecting a portion 'of the band originated at a given instant in accordance with the predominant frequencies thereof, and utilizing the selected portion of the -band to shift themessage band to a predev termined position in the frequency scale.

7. The method of message transmission,

-which comprises selecting a portion of` the 'message band in accordance with `the frequencies predominant therein at a given instant, utilizing the selected portion of the band to shift the message bandv to a predesaid sending 8. A circuit including a transmitter and a modulator for. shiftin the frequency of the original message ban a second modulator for reshifting the fre uency of said shifted band, a combination o selective circuits connected to said transmitter circuit each adapted to select different portions of the original message band, and means under the control of sai selective circuits for. controlling the oscillator lfrequency of saidwfirst modulator.

9. A circuit including a transmitter, and

a modulator for shifting the frequency of the original message band, a second modulator for reshifting the fre uency of said shifted band, a combinationof selective-circuits connected to said transmitter circuit each adapted to select different portions of the original message band, a delay network in said transmitter circuit between said selective circuits and said first modulator, a variable condenser under the control of said selective circuits, and a circuit controlled by said variable condenser and controlling the oscillator fre# quency of said first modulator.

10. A circuit including a transmitter and a modulator for shifting the frequency of the original message band, a second modulator for` reshifting the frequency of, said shifted band, an output circuit for ltransmitting said` reshifted band, a combination of selective circuits connected to said transmitter circuit each adapted to select different portions of the original message band, means under the 'control of said selective circuits for controlling the oscillator frequency of said'first modulator,a control channel connected to said output circuit, and means under the control of said selective circuits .for varying the chai'- acteristics of said control channel.

11. A transmission system comprising sending apparatus and receiving apparatus, afpparatus comprising means for shifting the requency of the o-rlginal mesvsage band in accordance with the frequencies redominant therein at a given instant, means for reshifting the frequency of said shifted band, and means for transmittingsaid reshifted band, said receiving apparatus comprising means for shifting the frequency of thereceived band, means `for reshifting the frequency of the shifted received band in 'ac- "cordance with the frequencies predominant lll) predominant therein at agiven instant, means shifted band, said receiving Vapparatus comprising means for shifting the frequency of the received band, means for reshifting the frequency of the shifted received band in ac? cordance with the frequencies predominant in the original message band at said given instant, and receiving means, and meansv for synchronizing the shifting at the sendingapparatus with the reshifting at the receiving apparatus.

13. A transmission system comprising sending apparatus and receiving apparatus,

'said sending apparatus comprising a circuit including a transmitter and a modulator for shifting the frequency of the original message band, a second modulator for reshifting the frequency of said shifting band, an output circuit for transmitting said reshifted and, a combination of selective circuits connected to said transmitter circuit each adapted to select diiferent portions ofthe original message band, means under the control of said selective circuits for controlling the oscillator frequency of saidfirst modulator, a control channel connected to-said output circuit, and means under thecontrol of said selective circuits for varying the characteristics of said control channel, said receiving a p aratus comprising an input .circuit inuding a modulatorfor shifting the -frequencyv of the received band, a second modu' lator for reshifting said .received shifted band, a receiver, andv means connected to said input circuit and responsive to said control-channel'for controlling the oscillator frequency of said second modulator.

In testimony whereof I have signed my name to this specification this 29th day of May, 1929.

HERMAN A. AFFEL.

reshifting the frequency of said shiftedy band, and means for transmitting said re- 

